You start with a plot of land, a run-down stable shack and one trusted mare. Everything after that is expansion, and the shape of your stable is really the shape of your strategy.
One horse and one shack is a deliberately small starting point. The early game is about whether you can cover one horse's care needs reliably while you work out the training loop, and the first real decision is not which building to buy but whether to buy a second animal or to improve the facilities for the one you have. For most players the facilities come first, because the first horse is your trial run for every system the rest of the game repeats.
Prize money from tournaments is the primary source of expansion funding, which means the growth of your farm is downstream of how well you compete. The loop is explicit in the design: compete, win, spend the winnings on more capacity, and then use that capacity to compete better. Buildings that raise stalls without raising training space, or the reverse, produce a stable that cannot actually run the horses it houses.
The central structural choice in the mid-game is whether the next big purchase is competition space or breeding space, because a single expansion budget cannot fund both and the game will not wait. Competing space makes the next season better and compounds through prize money. Breeding space makes every future horse better and compounds through genetics but on a much slower clock. Whichever you pick, the other does not get easier later — it just gets more expensive.